Microelectronic devices generally have a die (i.e., a chip) that includes integrated circuitry having a high density of very small components. In a typical process, a large number of dies are manufactured on a single wafer using many different processes that may be repeated at various stages (e.g., implanting, doping, photolithography, chemical vapor deposition, plasma vapor deposition, plating, planarizing, etching, etc.). The dies typically include an array of very small bond-pads electrically coupled to the integrated circuitry. The bond-pads are the external electrical contacts on the die through which the supply voltage, signals, etc., are transmitted to and from the integrated circuitry. The dies are then separated from one another (i.e., singulated) by backgrinding and cutting the wafer. After the wafer has been singulated, the individual dies are typically “packaged” to couple the bond-pads to a larger array of electrical terminals that can be more easily coupled to the various power supply lines, signal lines, and ground lines.
An individual die can be packaged by electrically coupling the bond-pads on the die to arrays of pins, ball-pads, or other types of electrical terminals, and then encapsulating the die to protect it from environmental factors (e.g., moisture, particulates, static electricity, and physical impact). For example, in one application, the bond-pads can be electrically connected to contacts on an interposer substrate that has an array of ball-pads. The die and a portion of the interposer substrate are then encapsulated with a covering.
Electronic products require packaged microelectronic devices to have an extremely high density of components in a very limited space. For example, the space available for memory devices, processors, displays, and other microelectronic components is quite limited in cell phones, PDAs, portable computers, and many other products. As such, there is a strong drive to reduce the height of the packaged microelectronic device and the surface area or “footprint” of the microelectronic device on a printed circuit board. Reducing the size of the microelectronic device is difficult because high performance microelectronic devices generally have more bond-pads, which result in larger ball-grid arrays and thus larger footprints.
Image sensor dies present additional packaging problems. Image sensor dies include an active area that is responsive to electromagnetic radiation. In packaging, it is important to cover and protect the active area without obstructing or distorting the passage of light or other electromagnetic radiation. Typically, an image sensor die is packaged by placing the die in a recess of a ceramic substrate and attaching a glass window to the substrate over the active area to hermetically seal the package. A vacuum is typically drawn to remove air from the gap between the image sensor die and the glass window. An inert gas can then be injected into the gap between the image sensor die and the glass window. One drawback of packaging image sensor dies in accordance with this method is the difficulty of removing dust, moisture, and other contaminants from the gap between the glass window and the image sensor die. Furthermore, the packaged image sensor dies are relatively bulky and, accordingly, use more space on a circuit board or other external device than other types of dies.
One existing approach to address the foregoing drawbacks is to attach a window directly to an image sensor die with a window support, such as an epoxy. In this approach a top portion of the window is machined to create a step to receive mold compound. The image sensor die is also attached to a die attach pad, and the bond-pads on the image sensor die are electrically coupled to leads that are positioned proximate to the ends of the image sensor die. The image sensor die, the die attach pad, and the step in the window are encapsulated. This approach, however, has several drawbacks. For example, the package does not effectively transfer heat away from the image sensor die because the leads are positioned proximate to the edge of the package. Moreover, the package has a high profile because the leads project outwardly away from the package. Furthermore, the mold compound does not effectively adhere to the die attach pad, and accordingly, separation can occur. In addition, machining the step in the window adds another procedure and expense to the manufacturing process.